1. Field of the Invention
The present invention relates to a working fluid for use in heat pump systems for air conditioners, refrigerators and the like in which one or a plurality of compressors, condensers, expansion devices, and evaporators are connected in service.
2. Description of the Related Art
Conventional heat pump systems for air conditioners and refrigerators have utilized as working fluids halogenated hydrocarbons derived from methane or ethane such as fluorinated hydrocarbons so-called freon (referred to as R.largecircle..largecircle., or R.largecircle..largecircle..largecircle. hereunder) which are generally used at temperatures in the range of about 0.degree. C. to about 50.degree. C. as condensation temperature and/or evaporation temperature, as well known in the art. Among them chlorodifluoromethane (CHClF.sub.2, R22, boiling point: -40.8.degree. C.) has been widely used as working fluid in domestic air conditioners, building air conditioners and large scale refrigerators.
However, the destruction of the ozone layer in the stratosphere with freon has in recent years become one of global environmental problems, and some fully halogenated hydrocarbons, for example, chlorofluorocarbons (CFCs) having a great stratosphere ozone depletion potential have already been regulated about their amounts to be used as well as to be produced under the Montreal Protocol and further there is a drift to inhibit the use and the production of CFCs in future. R22 has a trivial stratosphere ozone depletion potential of 0.05 based on the unity of ozone depletion potential (referred to as ODP hereunder) of trichlorofluoromethane and is not CFCs. However, R22 is expected to be increasingly used in future. Since refrigerators and air conditioners have been widely spread until now, the amount of R22 to be used and the production thereof are expected to increase so that they will have a great influence on the human life environment Therefore, there is an intensive need to develope substitutes for R22 which is able to destroy stratosphere ozone layer, though trivial in the ozone depletion potential, as early as possible.
The present invention has been derived to overcome the problems as described above and intends to provide a working fluid having little influence on the stratosphere ozone layer which may be used as a substitute for R22.
In order to achieve almost no influence on the stratosphere ozone layer, it is necessary to contain no chlorine in the molecular structure. As possible materials to satisfy this necessary condition there have been proposed fluorinated hydrocarbons containing no chlorine. The present invention proposes a mixture of fluorinated dimethylethers containing no chlorine. The dimethylethers are expressed hereunder as E.largecircle..largecircle..largecircle. where the number at the position next to the E represents the total of the number of carbon atoms minus one, the number at the second cipher after the E represents the total of the number of hydrogen atoms plus one, and the last cipher represents the number of fluorine atoms. One single candidate of such substitute working fluids is disclosed together with boiling points in W. L. Kopko, "Beyond CFCs: Extending the Search for New Refrigerants" ASHRAE's 1989 CFC Conf. pp. 39-46 (1989.9).
Prior art patents concerning with fluorinated ethers containing no chlorine are, for example, as follows: U.S. Pat. No. 2,066,905 describes trifluorodimethylether (E143, C.sub.2 H.sub.3 F.sub.3 O); U.S. Pat. No. 2,500,388 describes perfluorodimethyether (E116, CF.sub.3 --O--CHF.sub.2, bp. -59.degree. C.); U.S. Pat. No. 3,362,180 describes pentafluorodimethylether (E125, CF.sub.3 --O--CF.sub.2, bp. -35.degree. C.) and tetrafluorodimethylether (E134a, CF.sub.3 --O--CH.sub.2 F, bp. -20.degree. C.); U.S. Pat. No. 3,394,878 describes an azeotope of trifluorodimethylether (E143a, CF.sub.3 --O--CH.sub.3, bp. -23.degree. C.) and an azeotope of perfluorodimethyether (E116, CF.sub.3 --O--CF.sub.3, bp. -59.degree. C.); U.S. Pat. No. 3,409,555 describes a minimum boiling azeotope of trifluoromethyltrifluoroethylether (CF.sub.3 --O--CH.sub.2 --CF.sub.3, bp. +5.6.degree. C.) and dichlorofluoromethane (R21, bp. +9.degree. C.); U.S. Pat. No. 3,922,228 describes a maximum boiling azeotope of pentafluorodimethylether (E125, CF.sub.3 --O--CHF.sub.2, bp. -35.degree. C.) and dimethylether (E170, CH.sub.3 --O--CH.sub.3, bp. -24.degree. C.); U.S. Pat. No. 4,041,148 describes a mixture of bis-difluoromethylether (E134, CHF.sub.2 --O--CHF.sub.2, bp. +5.degree. C. ) and perfluorodimethylether (E116, CF.sub.3 --O--CF.sub.3, bp. -59.degree. C.); U.S. Pat. No. 4,139,607 describes a mixture of bis-difluoromethylether (E134, CHF.sub.2 --O--CHF.sub.2, bp. +5.degree. C.) and carbon dioxide gas (CO.sub.2); U.S. Pat. No. 4,783,276 describes a azeotope of dimethylether (E170, CH.sub.3 --O--CH.sub.3, bp. -24.degree. C.) and dichlorodifluoromethane (R12, bp. -30.degree. C.); U.S. Pat. No. 4,961,321 describes a mixture of bis-difluoromethylether (E134, CHF.sub.2 --O--CHF.sub.2, bp. +5.degree. C.) and fluorinated hydrocarbon containing no chlorine; U.S. Pat. No. 5,061,394 describes a maximum boiling azeotope of dimethylether (E170, CH.sub.3 --O--CH.sub.3, bp. -24.degree. C.) chlorotetrafluoroethane (R124, bp. -10.degree. C.); EP 443,912A describes a maximum boiling azeotope of dimethylether (E170, CH.sub.3 --O--CH.sub.3, bp. -24.degree. C.) and 1,1,1,2-tetrafluoroethane (R134a, bp. -27.degree. C.). However, these working fluids have a greately different boiling point from chlorodifluoromethane (R22, bp. -40.8.degree. C.) so that they can not be used as they are in the existing appliances using R22.